The game starts on the overworld of Earth 1423 BC. Immediately go to "Towne Linda" and buy a weapon and armor. The beginning is perhaps one of the most difficult parts of the game. Your first task now is to build up your character and get some gold. That means killing monsters. Well you are still rather weak and the monsters are strong and numerous. Remember to buy food in towns and Hitpoints from Lord British (using a time gate to get to his castle in 1990 AD) whenever necessary. You probably noticed that monsters not only leave some gold coins, but also some items. Thieves sometimes carry a "Blue Tassle" which you should get as soon as possible. But be careful when dealing with thieves. They tend to steal some items from you as well! When you have a "Blue Tassle" you must wait for a frigate. Don't fight the frigate! Board it instead. With the "Blue Tassle" the crew accepts you as their captain. With a frigate life gets MUCH easier, because 1. you can reach every single point on the overworld; 2. while on the ship you don't consume any food (except when you "Pass Time"); and 3. the guns are formidable weapons that kill enemies easily.
Sail around and kill monsters to get gold and items. Increase your amounts of Hitpoints and Food and buy a "Phaser" and "Power Armor". But mostlikely you won't be able to use the new weapon and armor yet, because your attributes are still too low. So the next task is to increase your attributes. There is only one place in the game where you can do this. Go to New San Antonio (1990 AD) and offer the clerk of the Hotel California 100 gold. If he says "Alakazam!", one of your attributes gets raised by 4 points (there is a chance that he doesn't say it, which means that you lost your gold). Which attribute he is raising can't be influenced. So spend some time killing monsters and increasing your attributes until you can at least wear "Power Armor" and use a "Phaser".
Now you are prepared for further adventures. There are still lots of things to do in New San Antonio. At first you should try to get the "Quicksword", the most powerful weapon in the game and the only one that can harm Minax. The fighter in the prison has it and will give it to you when you offer him 500 gold. But how to open the door to the cells (and all the other doors in towns)? Only the guards have the keys, but they won't give it to you. So fight some of them and make sure to leave the town early enough, because they are very strong. Reenter the town and enter the prison. Mostlikely you must kill a guard here again. Get the "Quicksword" and leave the town (avoiding the guards as best you can). If you don't succeed make sure to have more Hitpoints next time. 5000 should be enough though. Also in New San Antonio is an old man who has a special ring that lets you walk through force fields unharmed. But before he gives it to you, you must get "Father Antos'" blessing.
Father Antos lives on "Planet X". To get there you must get a rocket first. Go to "Pirate's Harbor" in Aftermath. To make your way over the ocean in Aftermath you must wait until a frigate appears or bring a plane (from "New San Antonio") via the time gates to Aftermath. Make sure you wear a "Reflect Suit" or "Power Armor" or you won't survive the upcoming space flight. Additionally you should carry enough "Tri-Lithiums" which is needed as fuel. In "Pirate's Harbor" board a rocket and hyperspace to coordinates 9-9-9 (more about space travel in the "Space-Section"). Land on "Planet X". You must land on grass; land anywhere else and you die. Enter "the castle and talk to Father Antos (he is in the chapel to the left) and receive his blessing. Fly back to Earth now (coordinates 6-6-6). Back to the old man in New San Antonio and offer him 500 gold. He then gives you the ring. With the ring, the "Quicksword" (make sure your "Agility" is high enough to use it) and lots of Hitpoints you are prepared to confront the evil sorceress Minax.
Enter the castle in the "Legend" time-zone. If you have much trouble with the monsters in the castle you should "Negate Time" (which requires a "Strange Coin"). Beware: There is an invincible Balron in the castle. Avoid fighting him at all costs (best with negating time). Minax is in the northeastern corner of the castle (Chamber One). When you hit her she teleports to the southwestern corner (Chamber Two). She constantly teleports between these two rooms, so follow her each time. After some blows she dies and you saved the world - again.